B.— CHEMISTRY 



37 



tetrahedral configuration of 3-covalent iodine. The trialkylphosphine 

 and trialkylarsine derivatives of aurous chloride and aureus iodide have, 

 however, the general molecular formula R3P(As)->AuCl(I) and the mole- 

 cule has probably a linear configuration. The trialkylphosphine-gold 

 compounds are remarkably stable and can be distilled at low pressures 

 without decomposition. On the other hand, Mann and his co-workers 

 have suggested that in the non-electrolytes, Et3P(NH3)2AuCl and 

 (EtO)3P(NH3)2AuCl prepared by Levi-Malvano (1908), the aurous gold 

 atom is 4-covalent, acquiring seven electrons and having an Eflrective 

 Atomic Number of 86, the atomic weight of radon, the next inert gas. 

 If this is the case these compounds are unique in the chemistry of gold ; 

 but it would appear that the determination of co-ordination numbers 

 from ammonia derivatives is not always satisfactory. Aurous com- 

 pounds having the compositions NHgAuCl, (NH3)2AuCl, (NH3)3AuCl 

 and even (NH3)i2AuCl have been described. Of these monoammino- 

 chlorogold and diamminoaurous chloride having the respective con- 

 stitutions : 



HaN^Au-Cl and [H3N-^Au^NH3]Cl 



are by far the most stable and in these compounds the aurous gold atom 

 is 2-covalent. The well-authenticated salts (NH3)4HC1 (Joannis 1902), 

 (NH3)4HBr (Bakhuis-Roozeboom 1885) and (NH3)4HN03 (Kuriloff 

 1898) may be compared with Levi-Malvano's compounds and with 

 triamminochlorogold. It would appear more doubtful that such com- 

 pounds afford evidence of the 4-covalency of hydrogen or aurous gold 

 rather than that they indicate the existence of chain formation of ammonia 

 molecules with links of co-ordinated hydrogen. If, however, by using 

 a more suitable co-ordinating compound than ammonia, it could be 

 established definitely that aurous gold may be 4-covalent as well as 2- 

 covalent, it would be interesting to determine whether such quadri- 

 covalent aurous compounds like the quadricovalent cuprous and argentous 

 compounds have a tetrahedral distribution of valencies. In this con- 

 nexion, the use of thioacetamide by Cox, Wardlaw and Webster 

 (1936) for the successful preparation of fefm^wthioacetamidocuprous 

 and fefr<2feVthioacetamidoargentous chlorides : 



r /CH, 



c=s 



►Cu(Ag) 



.NH, 



CI 



does not appear to give an analogous aurous gold compound. The only 

 aurous derivative of thioacetamide which Dr. F. H. Brain and I have 

 been able to isolate is the somewhat unstable tothioacetamidoaurous 

 bromide (1937) : 



'CH, 



CHal 



C=S-»Au^S=C 



NH, 



NH 



2.J 



Br 



